The present invention relates to domestic cooking ovens and particularly to combination microwave and electric self-cleaning ovens which are selectively operable in a plurality of operating modes including a microwave mode, a combined microwave/bake mode, a bake mode, a broil mode and a self-cleaning mode.
Domestic cooking ovens have been commercially available for a number of years having a cooking cavity which can be used for microwave cooking and combination microwave/bake cooking which uses microwave and thermal energy simultaneously, as well as the conventional baking and broiling. Such ovens also are equipped to provide an automatic self-cleaning cycle which uses the principle of pyrolysis for removing food soil and grease spatter from the inner walls of the cooking cavity. Such cleaning cycles decompose the soils and spatter by degrading them through exposure to high temperatures into gaseous products and carbon residue. The gaseous produces are then passed through an oxidation unit or catalytic smoke eliminator to further degrade the gases before they are returned to the ambient kitchen atmosphere.
For optimum operation of the oxidation unit, it is necessary to supply a small amount of oxygen in the form of room air into the oven cavity. Typically, a gap is provided in the door gasket which provides an otherwise essentially air-tight seal between the door and the cavity when the door is locked in its self-cleaning position. This small gap of predetermined size allows a regulated amount of air sufficient for satisfactory operation in the self-cleaning mode. The amount of air admitted to the cavity during self-cleaning is critical in order to avoid uncontrolled combustion which could occur at the high self-cleaning operating temperature if too much air entered the cavity. Thus, the inlet air passage is configured to admit only a controlled amount of air to the cavity when operating in the self-cleaning mode.
The small air inlet gap admits sufficient air to the cavity for baking, broiling and self-cleaning. However, microwave cooking tends, particularly with some foods such as baked potatoes, and cakes, etc., to generate a great deal of humidity in the cavity, and at a rate which is greater than the rate at which unassisted air enters the cavity through the closely regulated gap and escape from the cavity through the smoke eliminator outlet. As a result, a substantial amount of hot humid air tends to accumulate in the cavity until released by opening the oven door. In addition to the undesirable outrush of hot moist air when the door is opened, the moisture buildup causes condensation to occur on the walls of the cavity which presents potential rust problems.
One approach to solving this problem, as disclosed in U.S. Pat. No. 4,028,520 to S. H. Torrey, is to direct a portion of the magnetron cooling air through the waveguide into the cooking cavity. One drawback of this approach is that the magnetron blower must operate whenever the magnetron is operating. This adversely effects one of the more advantageous operating modes for combination ovens, namely, the microwave/bake mode in which radiant heat is used simultaneously with microwave energy to provide the browning associated with conventional baking and the short cooking time associated with microwave cooking. The continuous circulation of air in the cavity by the magnetron cooling fan when operating in this mode can greatly reduce operating efficiency by removing from the oven air heated by the bake element because magnetron cooling air flow is greater than needed to evacuate the oven. An additional drawback results from the fact that when air flow communication is provided between the waveguide and cavity, the waveguide cannot be tightly sealed from the cavity. Consequently, the air flow path provides a path for moisture condensing inside the oven to enter the waveguide which presents the potential for gradual deterioration of the waveguide due to oxidation over a period of time. Finally, it may also be desirable to blow cooling air over the magnetron during self-cleaning to prevent heat damage due to the extreme temperature in the cavity. To enable cooling air to be blown over the magnetron during the self-cleaning cycle, the portion of air flow directed into the cavity must be limited to the extent that venting the same portion during microwave operation may be less than satisfactory.
It would be desirable therefore to provide a venting arrangement for a combination microwave and electric self-cleaning oven which prevents the buildup of an undesirable amount of hot humid air in the cooking cavity when operating in the microwave and microwave/bake modes, by augmenting air flow through the cavity when needed to remove moist air but which otherwise limits air flow only to that needed for satisfactory operation in the self-cleaning mode and in which the waveguide is tightly sealed off from the cooking cavity so as to prevent moisture condensing in the cavity from entering the waveguide area.
It is therefore an object of the present invention to provide a combination microwave and electric self-cleaning oven with means for satisfactorily removing moist air on demand during operation in the microwave modes.
It is a further object of the present invention to provide a combination microwave and electric self-cleaning oven with means for removing moist air from the cavity when present during operating in the microwave modes, which means provides increased air flow through the cavity when conditions of high humidity exist to rapidly purge such air from the cavity while otherwise limiting air flow to a lesser rate compatible with operation in the bake, broil and self-cleaning modes of operation.
It is a further object of the present invention to provide a combination microwave and electric self-cleaning oven of the aforementioned type in which the waveguide area is tightly sealed to prevent moisture in the cavity from entering the waveguide area.